A systematic study of idiopathic thrombocytopenic purpura in childhood is underway in which measurements are being made of the amount of platelet-associated IgG on the platelets of affected children. Platelet associated IgG is measured quantitatively by a Fab-anti-Fab assay system. The amount of platelet associated IgG at oneset of disease will be correlated with prognosis for recovery and response to corticosteroid therapy. In chronic ITP, the amount of platelet associated IgG will be correlated with response to splenectomy. Attempts will be made to isolate and characterize the circulating anti-platelet antibody in acute ITP of childhood and to compare it with that in adults and in children with chronic ITP. BIBLIOGRAPHIC REFERENCE: McMillan, R., Luiken, G. A., Gordon, P., Lightsey, A. L., Gribble, T.J. and Schulman, I.: Platelet-associated IgG - an assay of antiplatelet antibody in immune thrombocytopenic purpura. Proc. Am. Soc. Hemat. Dallas, Texas, Dec. 1975, p. 80.